8/18/2019 Cell PCH -

1/13

Cell PCH

Some Questions answered

8/18/2019 Cell PCH -

2/13

CELL PCH

Q: What is Cell PCH State?

• CELL_PCH allows UE to remain in RRC Connected mode for

relatively long periods of time while minimizing the network and UE

resource reuirements!

• UE can "e paged in CELL_PCH# "ut the response must "e sent in

CELL_$%CH!

• &imilar to CELL_$%CH# the R'C keeps track of the individual cell

upon which the UE is camped

8/18/2019 Cell PCH -

3/13

Features:

• Uplink data transfer is not possi"le

• Paging (ype ) messages with a *R+ cycle are used for paging purposes

• Paging UE in CELL_PCH is more efficient than aging UE in !!C "dle

mode

• (ransitions to CELL_$%CH use the Cell Update procedure for more than

one reason

• (he UE and network resource reuirement is less than CELL_$%CH

• ,nter-system and inter-freuency cell reselections possi"le

• Radio access network uses U#!$%" to identify UE

CELL PCH

8/18/2019 Cell PCH -

4/13

$ow this must &e confusing' (ou must &e wondering

a&out the following:

•

.hat is U-R'(,/• How is UE paged in CELL_PCH state/

• How is CELL_PCH "etter than Cell ,dle 0ode

• How is signaling reduced with Cell_PCH/

&croll down to find the answers

CELL PCH

8/18/2019 Cell PCH -

5/13

Q: What is U#!$%"• ,n normal RRC ,dle mode# a UE is recognized "y its ,0&,# (0&,# or P-(0&,

• However in Cell *CH# Cell $%CH# CELL PCH and UR% PCH# the ,0&,#

(0&, are replaced "y U-R'(,! (he U-R'(, provides a uniue identifier for

the RRC connection within the PL0'!

• (he RRC Connection &etup message allocates a U-R'(,! U-R'(, is a

concatenation of the &R'C identity with the &-R'(,!

• ,n terms of P%1,'1# if the UE is in CELL_PCH or UR%_PCH# the (0&, is

replaced "y the U-R'(,!

• UE in CELL_$%CH are assigned a Cell Radio 'etwork (emporary ,dentifier

2C-R'(,3 in addition• to a U-R'(,! C-R'(, are assigned "y the controlling R'C to address the

UE within a specific cell!

CELL PCH

8/18/2019 Cell PCH -

6/13

CELL PCH

 The SRNC sends the TMSI and U-RNTI informationto the UE in the downlink RRC Connection SetuMessa!e"

8/18/2019 Cell PCH -

7/13

Q: How is a UE aged in Cell_PCH State?

•  % UE in CELL_PCH can "e paged using a Paging (ype ) message!

Paging (ype ) messages are transferred on the PCCH logical

channel and are used to page UE in RRC ,dle mode# CELL_PCHand UR%_PCH!

• (his is in contrast to Paging (ype 4 messages which are used to

page UE in CELL_*CH and CELL_$%CH!

• Paging (ype 4 messages do not include any indication of UE

identity "ecause they are transferred using the *CCH logicalchannel!

• ,f the UE is in CELL_PCH or UR%_PCH# the (0&, is replaced "y

the U-R'(,!

CELL PCH

8/18/2019 Cell PCH -

8/13

Q: How long does a UE sta) in Cell PCH State?

• ,nactive UE are typically maintained in CELL_PCH for 56 minutes

"efore returning them to RRC ,dle mode via CELL_$%CH!

• ,f UE are maintained in CELL_PCH for only a short period of time

there is an increased pro"a"ility that the end-user initiates a

su"seuent connection from RRC ,dle mode!

• (his would then involve a more comple7 and time-consumingconnection esta"lishment procedure# i!e! connection esta"lishment

delay is increased!

CELL PCH

8/18/2019 Cell PCH -

9/13

Q: How is Paging Load *timi+ed when using Cell_PCH state?

• We ,now that in "dle -ode Paging. all cells of a articular L/C

are aged

• "n general. Paging %)e 0 messages for UE in CELL_PCH are

directed towards onl) a single cell &ecause the !$C has

,nowledge of which cell each UE is camed uon' 

• (his means that the network paging load can "e decreased "y

allowing UE to remain in CELL_PCH rather than RRC ,dle mode!

• &croll down to find more details8!!

CELL PCH

8/18/2019 Cell PCH -

10/13

Q: How is Paging Load *timi+ed when using Cell_PCH state?

• (his scenario is illustrated in $igure in ne7t slide

•  9n the Right# the serving R'C 2R'C43 receives the paging

message from the C& core and directs it towards the appropriatecell!

• However# the second R'C 2R'C)3 also receives the paging

message and does not have any knowledge of where the UE is

located! (his R'C directs the paging message to all cells "elonging

to the location area! Consider this R'C "ehavior with a UE in RRC,dle 0ode!

• (he UE in Cell PCH state served "y R'C4 receives direct aging

message from the cell it is connected to

CELL PCH

8/18/2019 Cell PCH -

11/13

CELL PCH

Q: How is Paging Load *timi+ed when using Cell_PCH state?

8/18/2019 Cell PCH -

12/13

Q: Will the !!C signaling &e used when UE is in Cell_PCH state?

• $rom the network perspective# UE in CELL_PCH reuire the ,u-ps signaling

connection to "e maintained and to "e allocated logical R'C resources in

terms of a U-R'(,!

• (here are no dedicated resources on the air-interface# at the 'ode : nor onthe ,u"! .e e7pect to see less RRC %ttempts# hence# reduced signaling

• ,f a UE in CELL_PCH moved out of coverage and returned to RRC ,dle

mode as a result of failing to complete a periodic cell update then the R'C

would page the UE on a location area "asis rather than on a cell "asis!

•

(he R'C would also address the UE using its (0&,# P-(0&, or ,0&, ratherthan its U-R'(, which the UE would have deleted after returning to ,dle

mode!

CELL PCH

8/18/2019 Cell PCH -

13/13

 Thank #ou for readin!